In geology, obduction is the process where a tectonic plate lying under the ocean is pushed up over the top of an adjacent plate.
When an oceanic plate collides with a continental plate, it usually results in subduction, with the denser ocean crust sliding under the thick part of the earth's crust. Less often, obduction occurs, and the oceanic plate ends up on top. Geologists can tell this happened long ago from the presence of certain kinds of rocks and lava. In the U.S., the Appalachian Mountains were formed by obduction. The word's Latin roots are ob-, "toward," and ducere, "to lead."